Wave-signal direction finder



H. M. LEWIS WAVE-SIGNAL DIRECTION FINDER Filed May 23, 1942 2 Sheets-Sheet l $926 moEmwzuw H 553mm. 222 m ion 3 i ii T n W k m n i A H mm E mm 1 N u v K mm F||| ||||l|1||||||||||L A l INVENTOR HAROLD M. LEWIS BY mNEY April 2%, 1946. M E 2,397,746

WAVE- S IGNAL DIRECTION FINDER INVENTOR HAROLD M. LEWIS Patented Apr. 2, 1946 wnvn- SIGNAL pmrorron an Harold M. Lewis, Allenhurst, N. 3., assignor to Hazeltine Corporation, a corporation of Delaware 26 Claims.

This invention relates to direction finders and, more particularly, to direction finders of a type adapted to indicate the direction of a source of radiated wave signals.

A wave signal radiated from a source travels with a constant velocity and reaches listening posts or pick-up devices in the held of radiation with a time displacement determined by the relative orientation or difference in distance of the pickup devices with reference to the source. If the spacing between the pick-up devices is negligible in comparison with their spacing from the signal source, it may be assumed to a first approximation that the signals travel in parallel paths from the source to the pick-up devices. Based upon this assumption, it is possible to determine the direction of the source with reference to the pick-up devices from the time displacement of the signals picked up thereby. Further, by using several groups of pick-up devices, which groups are spaced a predetermined distance apart, the location of the signal source maybe determined. These principles have long been employed in the sound-ranging art and have also been embodied in direction finders utilized to locate high-frequency signal sources.

Thus, these prior-art arrangements frequently comprise means for indicating the phase-displacement of a signal received by a plurality'cf spaced pick-up devices. While arrangements of this type are satisfactory for certain applications, they do not provide a type of indication which is satisfactory under all conditions of operation. For example, when such prior-art arrangements receive signals radiated from a plurality of sources, it is not possible, under certain conditions, to determine the direction of a particular one of the sources with reference to the pick-up devices without supplementary and costly differentiating equipment.

It is an object of the invention, therefore, to-

provide an improved arrangement for determining the direction of a source of radiated signals which avoids one or more of the above-mew tioned disadvantages of the prior-art arrangements.

It is a further object of the invention to provide direction finder for determining the direction of a source of radiated wave signals comprises a pluralityv of spaced pick-up devices individually adapted to pick up the signals with a time-displacement determined by the relative orientation, or the relative distances, of the devices with reference to the source. The direction finder also comprises a signal-indicating apparatus including means for scanning a predetermined area and for producing within this scanned area an indication of any signal applied to the indicating apparatus over a period of time considerably longer than the period of the applied signal. The position of the indication within the scanned area is determined by the time of application of the signal with reference to the scanning of the area. Means are provided for applying the wave signals picked up by the devices to the apparatus to cause the apparatus to produce a two-dimensional signal pattern determined by the time displacement of the applied signals and representing the relative orientation of the devices with reference to the direction of the source or the direction of the source from the direction finder.

As used in this specification the term relative distances" is intended to mean difierence in distance.

In accordance with a feature of the invention the direction of a particular one of a plurality of radiated periodic signals is determined. To this end the pick-up devices of the above,-

described arrangement are individually adapted to pick up each of the radiated signals, whereby the indicating apparatus produces a plurality of signal patterns individually determined by the relative orientation of the devices with reference to the direction of one of the pluralit of sources, and means are provided for adjusting the indicating apparatus to cause the apparatus to produce a predetermined signal pattern determined by the relative orientation of the devices with reference to the particular one of the plurality of sources.

In accordance with a further feature of the invention, an arrangement for determining the location of a source of radiated wave signals comprises, a first plurality and a second plurality of pick-up devices, spaced a predetermined distance apart and associated with a signal-indicating apparatus as described above, whereby the apparatus is caused to produce a pair of signal patterns individually representing the relative orientation of the devices of each plurality with refer ence to the direction of the source.

, This invention may be employed for determining the direction of any source of radiated periodic signals, but is particularly adapted for determinlng the direction of a machine gun that is firing at a substantially constant firing rate,

Such a gun is a source of radiated periodic signals of pulse wave form which may be received by the spaced pick-up devices and applied to the indicating apparatus to produce the above-discussed signal patterns. In this connection it will be understood that the direction finder of this invention is also peculiarly adapted to determine the direction of a particular one of a plurality of machine guns which have firing rates so related to one another that frequency-selective arrangements are not capable of separatin the radiated signals.

For a better understanding of the invention,

' together with other and further objects thereof,

reference lshad to the following descriptiontaken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

Fig. 1 of the drawings is a circuit diagram,

partly-schematic, of a direction finder in accordance with the invention which is used for determining the direction of a source of radiated periodic signals; Fig. 2, is a schematic diagram of a portion of the arrangement of Fig. 1 utilized in explaining the operation of that arrangement of the invention; Figs. 3, 4, and 5 represent signal patterns produced by the arrangement o'fFig. 1 under various operating conditions; Fig. 6 represents a modified arrangement of the invention; and Fig. 7 is a circuit diagram of a peak-rectifying means which may be included in the arrangements of Figsl 1 and 6 to facilitate locating the source of a radiated signal having a sinusoidal or similar wave form,

Referring now more particularly, to the drawings there is illustrated in Fig. 1 a direction finder in accordance with the invention for determining the direction of a source of radiated periodic signals comprising a plurality of spaced pick-up devices individually adapted to pick up the signals with a time-displacement determined by the relative orientation of the devices with reference to the direction of the source. Specifically the arrangement comprises a pair'of microphones or sound-signal pick-up devices ii and i2, the output circuits of which are individually coupled to adjustable gain amplifiers 'l3 and I 4, respectively, which comprise means for distinguishing the output signals of each of the'pick-up devices. The pick-up devices and their associated amplifiers are suitably secured to the opposite ends of a hollow T-shaped supporting standard l5 whereby the pick-up devices are spaced a predetermined distance apart. The spacing of the pick-up devices with reference to one another is negligible in comparison with their distance from the source of radiated periodic signals and thus the parallel arrows S1, S2, representing a signal receivedby the. pick-up devices l2 and M, respectively, indicate the relative orientation of the devices, or the relationship of the line of centers of the devices, with reference to the direction of this particular signal source.

.The arrangement also comprises a signal-indicating apparatus 20 including means for indicatin signals applied thereto, over a period of time considerably longer than the period of the applied signals, in a two-dimensional signal pattern determined by the time-displacement of the applied signals. In particular, the recording apparatus is of the cathode-ray typeincluding a screen, means for producing an electron beam and for causing the beam to scan the screen in v a two-dimensional pattern, and means including a control electrode for modulating the beam in accordance with signals applied to the apparatus. The cathode-ray tube 2| thus includes a fluorescent screen 22, a control electrode 29, and an electrode system comprising cathode 23 and anode 24 for producing an electron beam and accelerating it to the screen 22 in a well-known and conventional manner. A pair of electros..atic deflecting plates 25, to which saw-tooth scanning waves generated in a line-scanning generator 26 are applied, serve to deflect the electron beam in a first direction at a predetermined line-scanning frequency and a second pair of electrostatic deflecting plates 21, to which scanning waves generated in field-scanning generator 28 are applied, serve to deflect the beam in a second direction normal thereto-at a predetermined fieldscanning frequency, whereby the beam is caused to scan the screen 22 in a series of fields of parallel lines. For the particular arrangement under consideration, deflectin plates 25 and 21 deflect the electron beam in horizontal and vertical directions, respectively.

Means are provided for adjusting the signalindicating apparatus and to this end the linescanning generator 26 includes means for adjusting the frequency of the saw-tooth scanning voltage supplied thereby to the electrostatic defleeting plates 25 to adjust the line-scanning frequency of the apparatus 20. Thus, the line-scanof the above-identified patent. It may be seen that this generator comprises a condenser C which is charged by battery E through a constant-current device H. A vacuum tube S is coupled across condenser C and the input circuit of a feed-back of line-scanning generator 2% is applied, is coupled to the field-scanning generator 28 properly to synchronize the scanning voltages applied to the cathode-ray tube 2 i, in a well-known manner.

In-order that the indicating apparatus mlmay produce a signal pattern representing the relative orientation of the devices M, l2 with reference to the direction of the signal source, means are included in the arrangement of Fig. 1 for applying the signals picked up by each of the devices H, IE to the control electrode 29 of the indicating apparatus. For this purpose, the output signals of the devices, after being selectively amplified in amplifiers l3 and M, are applied by way of conductors 32, 32 and coupling condenser 33 to the control electrode 29 of the cathode-ray tube 2|.

In considering the operation of the arrangement as thus far described, it will be assumed that the parallel arrows S1, S2. represent a signal of pulse wave form having a predetermined periodicity radiated from a source whose direction it is desired to determine. Further, it will be assumed that line-scanning generator 26 is adjusted so that the line-scanning frequency of apparatus is not substantially diflerent from an integral multiple of the periodicity of the received radiated signal. In operation, it will be seen that, when the voltage across condenser C has reached a predetermined value, tube S be= comes conductive. 'The voltage drop across the anode load of tube S applies a negative voltage pulse to the control electrode of the feed-back tube Rv which, in turn, applies a positive pulse to the control electrode of tube S increasing its conductivity and causing a rapid discharge of the condenser C. Thus, a saw-tooth voltage wave is developed across condenser C. The frequency of the developed voltage is controllable. by adjustments of the tap f, as explained in the reference patentand it will be understood that generator 2G is preferably a calibrated oscillator including means (not shown) for indicating the frequency of. the generated oscillations. The orientation of the pick-up devices with reference to the direction of the source is, under the conditions assumed, such that one, namely microphone H, is closer to the signal source than the other. Thus, the radiated signal is received by pick-up device .l l a predetermined period of time before it is received by device 62 whereby there is applied to the control electrode 29 of the indicating apparatus 20 a succession of spaced pairs of signal pulses having a periodicity corresponding to the periodicity of the received radiated signals and having a spacing indicative of the phase delay of the signal as received by the pickup devices. This succession of pairs of signal pulses modulates the electron beam of the scanning apparatus as it scans screen 22 thereof in a series of fields of parallel lines, whereby there is produced in a field on screen 22 a two-dimensional signal pattern, represented in Fig. 3, comprising a plurality of parallel rows of signal indicia M, N representing the relative orientation of the pick-up devices with reference to the direction of the assumed signal source. It will be understood that screen 22 hears a suitable calibration (not shown) whereby the linear separation of the rows of signal indicia may be easily determined. Knowing the line-scanning irequency of the recording apparatus, the phase delay of the signal as received by the pick-up devices may be easily computed from the separation of the rows of signal indicia from which the direction of the signal source with reference to the pick-up devices may be determined, in a manner presently to be described.

In Fig. 2, the pick-up devices it and i2 are again represented, the spacing therebetween being represented by the known'distance x-y. Knowing the phase delay of the signal received by the piclr-up devices and the velocity of wave propagation under any given operating conditions, the difference in the distances of the microphones from the signal source may be computed. Using this distance as a radius and the point a: as a center, a circle is drawn and a tangent drawn to that circle from the point 11, thereby determining the point a of Fig. 2 and defining the direction right-triangle eye. The hypotenuse a:-y and the side :r-z of the triangle have known values from which the angle 21:11 may be deter- 3 be determined by scribing the circle about the point 1 and drawing a tangent thereto from the point :r. In order to avoid this ambiguity, one of the amplifiers l3, I4 is adjusted to have a considerably higher gain than that of the other so that each oi the rows of signal indicia M, N may be definitely associated with one of the pick-up devices. In the specific arrangement under discussion, amplifier I3 is assumed to have the higher gain whereby the spots comprising the row M of signal indicia of Fig. 3 appear brighter on the screen 22 than those comprising the row N. Hence, upon inspection of the signal pattern, it may be determined that the pulses from device II lead those 01 device l2 and that the latter is the more remote from the signal source. Con- A reference to the direction of the source.

mined. The line :c-y of the microphone has a given direction with reference to north as indicated by the direction arrow win Fig. 2, and hence the angle wxz representing the direction of the signal source with reference to north may easily be computed.

Obviously, a conjugate signal direction may sequently, the angle wmz of Fig. 2 represents the true direction of the signal source with reference to the pick-up devices and with reference to north.

In order to obviate the necessity for computing the direction of the signal source with reference to the pick-up devices, means are provided to enable a direct reading or indication of the direction of the signal source to be obtained. Consequently, the arrangement of Fig. 1 includes means for adjusting the relative orientation of the devices with reference to the direction of the source to cause ti 2 signal-indicating apparatus to produce a par icular signal pattern representing a predetermii. ed orientation of the devices with For this purpose the vertical section of the microphone support I5 is rotatably supported within a bushing i6 mounted within a tripod standard H which supports the entire assembly. A pointer is secured to the vertical portion of the support l5 and a direction scale it secured to the tripod ll comprise means for obtaining from predetermined orientations of the devices with reference to the signal source a direct indication of the direction of the source.

In considering the operation of the arrangement when the orientation of the pick-up devices is rendered adjustable with reference to the direction of the signal source as just described, it will be understood that the signal pattern illustrated in Fig. 3 comprising the parallel rows of signal indicia M, N again represents the relative orientation of thepick-up devices with reference to the direction of the source. By rotating the standard is, the relative orientation of the pickup devices with reference to the direction of the signal source is varied, whereby the spacing of the parallel rows of signal indicia produced on screen 22 is also varied. It may be seen that as the support i5 is rotated through 360 degrees, this spacing of the rows of signal indicia varies between two limiting positions each of which represents a predetermined orientation of the pick-up devices with reference to the direction of the source. In one of these limiting positions the pulses from the pick-mp devices are reproduced in superposed relation on the screen or, in other words, the parallel rows of signal indicia M, N merge into a single row of signal indicia indicated as O in Fig. 3. Such a signal pattern indicates that the pick-up devices are equidistant from the signal source and an azimuth reading obtained from scale lg indicates the true direction of the signal source. In the other of the limiting positions the rows of signal indicia have a maximum separation as represented by the rows M, N in Fig. 3. such a signal pattern is obtained when the pick-up devices are in direct alignment with the direction of the signal source and in this position of the pick-up devices a direct reading may again be obtained from the scale is representing the azimuth direction of the source.

By way of summation, it will be seen that the direction finder of Fig. l for determining the direction of a source of periodic radiated wave signal comprises a plurality of spaced pickup devices ll, l2. Each device is adapted to pick up the periodic signals with a time displacement determined by the relative distances of the devices with reference to the signal source. The electrode structure of the cathode-ray tube of indicating apparatus 20 as well as the scanning generators 26 and 28 comprise means for scanning a predetermined area, namely the screen 22, and for producing within the scanned area an indication of any signal applied to, the indicating apparatus over a period of time considerably longer than the period of the applied signal. The position of the resulting indication within the scanned area is determined by the time of application of the applied signal with reference to scanning of the scanned area. The coupling elements 32, 33 interposed between the pickup devices and the in;- dicating apparatus 2@ constitute means for applying the wave signals picked up by the devices H, l2 to apparatus 20 to cause the apparatus to produce a two-dimensional signal pattern. This twodimensional pattern is determined by the time displacement of the signals as applied from devices ii, i2 and represents the direction of the signal source with reference to thedirection finder.

The above-described arrangement may also be employed for determining the direction of aparticular one of a plurality of sources of radiated periodic signals. In considering the operation of the arrangement to accomplish this result, it will be assumed that the parallel broken arrows S: and S4 of Fig. 1 represent a second radiated signal having a periodicity different from that of the first radiated signal and that both such signals are picked up by the devices H and J2. It will be clear from the above description that under this condition of operation the indicating apparatus is caused to produce a plurality of signalpatterns individually representingthe relative orientation of the devices ll, i2 with reference to the direction of one of the plurality of sources. Thus, as indicated in Fig. 4, the indicating apparatus produces a first signal pattern comprising parallel rows of signal indicia M, N, representing the relative orientation of the pick-up devices with reference to the direction of the first-mentioned signal, and a second signal pattern comprising the parallel rows of signal indicia P, Q representing the relative orientation of the devices with reference to the second-mentioned signal. From these signal patterns it is possible to determine the direction of either or both of the signal sources even though the frequencies of the received signals are so closely related that the signals cannot effectively be separated by way of a frequencyselective arrangement. Thus, an advantage of the direction finder of this invention over those of the prior art becomes apparent at once for, with prior-art arrangements, when signals from a plurality of sources are being received, it is common practiceto rely on a discriminator, such as a frequency-responsive arrangement, to separate the signals, radiated from the source to be located. from the other received signals.

With a plurality of such signal patterns produced on the screen, however, it is frequently difficult to identify the pattern representing a particular one of the plurality of signals, the direction of which it is desired to determine. In

accordance with the present invention, however;

if the periodicity of the desired signal is known, the frequency of a scanning component of the apparatus 20 can be adjusted with reference thereto whereby the apparatus is caused to produce a predetermined signal pattern representing the relative orientation of the devices with reference to the particular source, Specifically, the line-scanning generator 26 may be adjusted to cause the line-scanning frequency of the recording apparatus to be approximately an integral multiple of the periodicity of the desired signal, whereby the signal pattern produced on screen 22 representing the relative orientation of the devices ll, 12 with reference to the direction of that particular source, comprises a pair of substantially vertical and parallel rows of signal indicia M", N" as indicated in Fig. 5. From this signal pattern the direction of the particular source may be determined in a manner already described.

Obviously, in addition to adjusting the linescanning frequency whereby the desired signal pattern is easily identified, the orientation of the pick-up devices with reference to the direction of the particular source maybe varied further to modify the signal pattern for the particular source and permit a direct reading from the calibration IQ of the directionof the source. This expedient is resorted to particularly when the plurality of. received signals have the same periodicity, in which case the adjustment of the line- I scanning frequency causes each of the plurality of signal patterns produced on screen 22 to comprise a" pair of vertical rows of signal indicia. Under this operating condition, by adjusting the orientation of the pick-up devices, the signal pattern of a particular source may readily be difierentiated from the other signal patterns on the screen.

In considering the signal patterns-represented by the relative periodicities of the received signal and the line-scanning component. Thus the'rows M, N represent an operating condition in which theline-Scanning frequency is slightly greater than an integral multiple of the periodicity of received periodic signal; rows M", N" represent an operating condition in which the line-scanning frequency is substantially equal to an integral multiple of the periodicity of the received periodic signal; and rows P, Q represent an operating condition in which the line-scanning frequency is slightly less than an integral multiple pf the periodicity of the received periodic signal. It will be understood'that the term "integral multiple as used in this specification is intended to include the condition in which the integral is one or line-.-scanning takes place along sloping lines due to the concurrent field-scanning efiect. However,

in most applications the line-scanning frequency is so high with reference to the field-scanning frequency that the line-scanning operation may be considered to be along horizontal lines, as-

illustrated. 5 N

In Fig. 6 there is disclosed an arrangement in accordance with the present invention for determining the location of ,a source of radiated periodic signals; The arrangement of Fig. 6 in efl'ect includes two direction finders of the general type illustrated in Fig. l and thus comprises a second plurality of spaced pick-up devices i l, i 2', spaced a predetermined distanced from the pick-up devices ii, I 2, and, comprising suitable indicating apparatus coupled thereto. Each pair of pick-up devices of Fig. 6 comprises an arrangement identical to the arrangement described in connection with Fig. i and corresponding elements bear the same reference numerals, the reference numerals of the elements of the second pair of pick-up devices being primed. The signal-recording means of Fig. 6 comprises a pair of synchronously operated cathode-ray type signal-indicating apparatus 2 i. 2 i each of which has means of the type included in the arrangement of Fig. 1 for indicating the signals applied thereto in a two-dimensional signal pattern determined by the time-displacement of the applied signals. The apparatus 2! and 2! are controlled and synchfoni y way of line-scanning generator 26, field-scanning generator 28, and frequency divider 30 in the manner already described inconnection with the indicating apparatus 20.

In considering the operation of this arrangement, it will be assumed that the parallel arrows S1 and Sr represent periodic signals radiated from a source and received by devices l2 and H, re-' spectively, and that the parallel arrows S1 and S2 represent the same signals as received by pickup devices I2, I i, respectively. In the manner already described, the signals picked up by each of the pairs of pick-up devices are applied to one of the indicating apparatus whereby each apparatus is caused to produce a signal pattern representing the relative orientation of the devices of one of these pairs with reference to the source. From the signal patterns thusproduced the direction of the signal source with reference to each of the pluralities of pick-up devices may be computed. This direction may also be obtained by adjusting the relative orientation of each of the pairs of devices to cause the signal-indicating apparatus to produce predetermined signal patterns representing predetermined orientations of the devices of each with reference to the direction of indicating apparatus in the above-described arrangement to determine the location of a signal source, it will be understood that, if desired, a

single indicating apparatus may be utilized.

7 re resenting the direction of said source with With such an arrangement a'pair of signal patterns individually representing the relative orientation of the devices of one pair with refer ence to the direction of the source is reproduced. Then. by adjusting the orientation of the devices of one pair, the signal patterns may conveniently be associated with each of the spaced pairs of pick-up devices and thus the direction of the source with reference to each pair of devices easily determined.

The direction filldfilflOf this invention is also capable of determining the direction of a source of a radiated periodic signal having a sinusoidal, or other wave shape, as distinguished from a pulse wave form. It is only necessary in such 1 an application that means be associated with the pick-up devices H, l2 for deriving periodic pulses.

from a received wave. To this end the output circuits of units l3 and I4 may be individually coupled to a pair of peak-rectifying means of the type illustrated in Fig. 7 which, in a manner well understood in the art, derive periodic pulses from the received signals. Each such peak rectifier may comprise a pair ofinput terminals A-B, a condenser 41a leak resistor 4|, a diode 42, a load resistor 33, and a pair of output terminals C-D.

The values of condenser and resistor 4| are so chosen as to give the rectifier circuit a time constantthat is long compared with the period of the receivedsignal. The circuit and operation of 25 the peak rectifier of Fig. '7, per see, are well understood by those skilled in the art. Thus, the direction of a shipmay readily be determined with,

the above-described direction finder since the ship' propeller radiates ensignal having a subac stantially sinusoidal wave form which may be received .by the pick-up devices andpeak-rectified to deliver periodic pulses to the recording apparatus. It will be understood that the direction of an airplane may be determined in a similar 86 manner.

It will also be understood that the principles or the invention are applicable to light ranging as well as sound ranging. In such case, photo cells may be substituted for the microphones in- $9 the system.

may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes andmodifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A direction finder for determining the direction of a source of radiated wave signals comprising, a plurality of spaced pick-up devices individually adapted to pick up said signals with a time-displacement determined by the relative distances of said devices with reference to said source, a signal-indicating apparatus including means for scanning a predetermined area and for producing within said area an indication of 50 any signal applied to said apparatus over a period of time considerably longer than the period of said signal, the position of said indication within said area being determined by the time of application of said signal with reference to the scanning of said area, and means for applying the wave signals picked up by said devices to said apparatus to cause said apparatus to produce a two-dimensional signal pattern determined by the time displacement of said applied signals and reference to said direction finder. r 2. A direction finder for determining the direction of a source of radiated periodic signals comprising, a plurality of spaced pick-up devices individually adapted to pick up said signals with a time-displacement determined by the relative orientation of said devices with reference to the direction of said source, a signal-indicating apparatusi including means for scanning a predetermined area and for producing within said area an indication of any signal applied to said appa ratus over a period of time considerably longer than the period of said signal, the position of said indication within said area being determined ,by the time of application of said signal with reference to the scanning of said area, and means for applying the periodic signals picked up by said devices to said apparatus to cause said apparatus to produce a two-dimensional signal pattern determined by the time-displacement of said applied signals and representing the relative orientation of said devices withrefere'nce to the paratus over a period of time considerably longer than the period of said signal, the position of by the time of application of said signal with reference to the scanning of said area, and means for applying the pulses picked up by said devices 30 said apparatus to cause said apparatus to proluce a two-dimensional signal pattern deterrrined by the time-displacement of said applied pulses and representing the relative orientation ofsaid devices with reference .to the direction of said source.

4. A direction finder for determining the direction of a source of radiated periodic signals comprising,'a plurality of spaced pick-up devices individually adapted to pick up the signals witha time-displacement determined by the relative orientation of said devices with reference to the direction of said source, means associated with said indication within said area being determined said pick-up devices for deriving periodic pulses from said received signals, a signal-indicating apparatus including means for scanning a predetermined area and for producing within said area an indication of any signal applied to said apparatus over a period of time considerably longer than the period of said signal, the position of said indication within said area being deter-' mined by the time of application of said signal with reference to the scanning of said area, and means for applying said periodic pulses to said apparatus to cause said apparatus to produce a two-dimensional signal pattern determined by the time-displacement of said applied pulses and representing the relative orientation of said devices with reference to the direction of said source.

5. A direction finder for determining the direction of-a source of radiated periodic signals comprising; a plurality of spaced pick-up devices individually adapted to pick up said signals with a time-displacement determinedby the relative orientation of said devices with reference to the direction of said source, peak-rectifying means associated with said pick-up devices for deriving periodic pulses from said received signals, a signal-indicating apparatus including means for scanning a predetermined area and for producing within said area an indication of any signal applied to said apparatus over a period of time considerably longer than the period of said signal, the position of said indication within said area being determined by the time of application of said signal with reference to the scanning of said area, and means for applying said periodic pulses to said apparatus to cause said apparatus to produce a two-dimensional signal pattern determined by the time-displacement of said applied pulses and representingthe relative orientation of said devices with reference to the direction of said source.

6. A direction finder for determining the direction of a source of radiated and periodic sound signals comprising, a plurality of spaced soundsignal pick-up devices individually adapted to pick up said signals with a time-displacement determined by the relative orientation of said devices with reference to the direction of said source, a signal-indicating apparatus including means for scanning a predetermined area and for producing within said area an indication of any signal applied to said apparatus over a period of time considerably longer than the period of said signal, the position of said indication within said area being determined by the time of application of said signal with reference to the scanning or said area, and means for applying the signals picked up by said devices to said apparatus to cause said apparatus to produce atwo-dimen sional signal pattern determined by the timedisplacement of said applied signals and representing the relative orientation of said devices with reference to the direction of said source.

7. A direction finder for determining the direction of a source of radiated periodic signals comprising, a plurality of spaced pick-up devices individually adapted to pick up said signals with a time-displacement determined by the relative orientation of said devices with reference to the direction of said source, a signal-indicating apparatus including means for scanning 'a predetermined area and for producing within said area an indication of any signal applied to said apparatus over a period of time considerably longer than the period of said signal, the position of said indication within said area being determined by the time of application of said signal with reference,to the scanning of said area, meansv for applying the signals picked up by said devices to said apparatus to cause said apparatus to'produce a two-dimensional signal pattern determined by the time-displacement of said applied signals and representingthe relative orientation of aid devices with reference to the direction of aid source, and means for causing the output signals of said devices to be distinguishable. i

8. A direction finder for determining the direction of a source of radiated periodic signals comprising, a plurality of spaced pick-up devices individually adapted to pick up said signals with a time-displacement determined by the relative orientation of said devices with reference to the direction of said source, a signal-indicating apparatus including means for scanning a predetermined area and for producing within said area an indication of any signal applied to said apparatus overa period of time considerably longer than the period of said signal, the position of, said indication within said area being determined by the time of application of said signal with reference to thescanning of said area, means for applying the signals picked up by said devices to said apparatus to cause said apparatus to produce a twodimensional signal pattern determined by the time-displacement of said applied signals and representing the relative orientation of saiddevices wit reference to the direction of said source, and mea s comprising a plurality of adjustablegain amplifiers individually connected with said pick-up devices for causing the output signals of mined area and for producing within said area an indication of any signal applied to said apparatus over a period of time considerably longer than the period of said signal, the position of said indication within said area being determined by the time of application of said signal with reference to the scanning of said area-and means for applying the signals picked up by said devices to said apparatus to cause said apparatus to pro-v duce a two-dimensional signal pattern comprising a "row of signal indicia for each of said devices spaced in said scanned area in accordance with the relative orientation of said devices with reference to the direction of said source.

10. A direction finder for determining the direction of a source of radiated periodic signals comprising, a plurality of spaced pick-up devices individually adapted to pick up said signals with a time-displacement determined by the relative orientation of said devices with reference to the direction of said source, a cathode-ray type signal-indicating apparatus including means for scanning a predetermined area and for producing within said area an indication of any signal applied to said apparatus over a period of time considerably longer than the period of said signal, the position of said indication within said area "being determined by the time of application of said signal with reference to the scanning of said area, and means for applying the signals picked up by said devices to said apparatus to cause said apparatus to produce a two-dimensional sigma;

,. pattern determined by the time-displacement said applied signals and representing the relative orientation of said devices with reference to said source. i

11. A direction finder for determining the direction of a source of radiated periodic, signals comprising, a plurality of spaced pick-up devices individually adapted to pick up said signals with a time-displacement determined by the relative orientation of said devices with reference to the direction of said source, a cathode-ray type sigmil-indicating apparatus including a screen, means for producing an electron beam and for causing saidbea-m to scan said screen in a twodimensional pattern, means including a control electrode for modulating said beam in accordance with any signal applied to said apparatus .over a period of time considerably longer than the period of said signal to produce an indication positioned on said screen in accordance with the time of application of said signal withreference to the asa'avec i 7 12. a direction finder IO! determining the direction of a source of radiated periodic signals mprising. a plurality of spaced pick-rip devices individually adapted to pick up said signals with a time-displacement determined by the relative i agentation of said devices with reference to the action of said source, a signal-indicating apparatus including means for scanning a predetermined area and for producing within said area an indication of any signal applied to said apparatus over a period of time considerably longer than the period or said signal, the position of said indication within said area being determined by the time of application of said signal with reference to the scanning of said area, means for applying the signals picked'up by said devices to said apparatus to cause said apparatus to produce a two-dimensional signal pattern determined by the time-displacement of said applied signals and representing the relative orientation of said devices with reference to the direction of said source, and means for adjusting the relative orientation of said devices with reference to the direction of said sourpe to cause said apparatus to produce a particular signal pattern representing a predetermined orientation of said devices with reference to the direction or said source.

13. A direction finder for determining the direction of a source of radiated periodic signals comprising, a plurality of spaced pick-up devices individually adapted to pick up said signals with a time displacement determined by the relative orientation of said devices with reference to the direction of said source, a signal-indicating apparatus including means for scanning a predetermined area and for producing within said area an indication of any-signal applied to said apparatus over a period of time considerably longer than the period of said signal, the position of said indication within said area being determined by the time of application of said signal with reference to the scanning of said area, means for applying the signals picked up by said devices to said apparatus to cause said apparatus to produce a 1 representing the relative orientation of said devices with reference to the direction of said source, means 'for adjusting the relative orientation of said devices with reference to-the direction of said source to cause said apparatus to produce a particular signal pattern representing a predetermined orientation of said devices with ref-' erence to the direction of said source, and means for obtaining from said predetermined orientation a. direct indication of the direction of said source.

14. A direction finder for determining the direction of a source of radiated periodic signals comprising, a plurality of spaced pick-up devices individually adapted to pick up said signals with a time-displacement determined by the relative orientation of said devices with reference to the scanning ofsaid screen, and means for applying representing the relative orientation of said de-" vices with reference to the direction of said source.

direction of said source, a signal-indicating apparatus including means for scanning a predetermined area and for producing within said area an indication of any signal applied to said apparatus over a period of time considerably longer than the period of said signal, the position of said indication within said area being determined by the time of application of said signal wth reference to the scanning of said area, means for applying the signals picked up by said devices to said apparatus to cause said apparatus to produce a two-dimensional signal pattern comprising a plurality of parallel rows of signal indicia representing the relative orientation of said devices .of signal indicia for said plurality of rows and representing a predetermined orientation of said devices with reference to the direction of said source.

15. A direction finder for determining the direction of a source of radiated periodic signals comprising, a plurality of spaced pick-up devices individually adapted to pick up said signals with a time-displacement determined by the relative orientation of said devices with reference to the drection of said source, a signal-indicating apparatus including means for scanning a predetermined area and for producing withinsaid area an indication of any signal applied to said apparatus over a period of time considerably longer than the period of said signal, the position of said indication within said area being determined by the time of application of said signal with reference to the scanning of said area, means for applying the signals picked up by said devices to said apparatus to cause said apparatus to produce a two-dimensional signal pattern comprising a plurality of parallel rows of. signal indicia repreorientation of said devices with reference to the direction of each of said plurality of sources, a signal-indicating apparatus including means for scanning a predetermined area. at a predetermined scanning frequency and for producing within said area' an indication of any signal applied to said apparatus over a period" of time considerably longer than the period of said signal, the position of said indication within said 10 area being determined by the time of application of said signal with reference to the scanning of said area, means for applying the signals picked up by said devices tosaid apparatus to cause said apparatus to produce a plurality of two-dimensional ,signal patterns determined by the timedisplacement of said applied signals and individually representing the relative orientation of said devices with reference to the direction of ,one of saidtplurality of sources, and means for adjusting said scanning frequency to cause said apparatus to produce a predetermined signal pattern representing the relative orientation of said devices with reference to the direction of said particular one of said plurality ofsources.

18. A direction finder for determining the direction of a particular one of a plurality of sources of radiated periodic signals comprising, a plurality of spaced pick-up devices individually adapted to pick up each of said signals with a time-displacement determined by the relative senting the relative orientation of said devices with reference to the direction of said source, and

means for adjusting the relative orientation of said devices with reference to the direction of said sourceito cause said apparatus to produce a particular signal pattern comprising a plurality of parallel rows of signal in icia having maximum separation and represent ng a predetermined orientation of said devices with reference to the direction of said source.

16. A direction finder for determining the direction of a. particular one of a plurality of sources on radiated periodic signals comprising, a plurality of spaced pick-up devices individually adapted to pick up each of said signals with a time-displacement determined by the relative orientation of said devices with reference to the direction of each of said plurality of sources, a

signal-indicating apparatus including means for scanning a predetermined area and for producing within said area an indication of any signal applied to said apparatus over a period of time considerably longer than the period of said signal, the position of said indication within saidarea being determined by the time of application of said signal with reference to the scanning of said area, means for applying the signals picked up by said devices to said apparatus to cause said apparatus to produce a plurality of two-dimensional signalpatterns determined by the timedisplacement' of saidv applied signals and individually representing the relative orientation of said devices with reference to the direction of one of said plurality of sources, and-means for adjusting said apparatus to cause said apparatus to produce a predetermined signal pattern representing the relative orientation of said devices .with reference to the direction of said particular one, of said plurality of sources.

17. A direction finder for determining the direction of a particular one of a plurality of sources of radiated periodic signals comprising, a plurality of spaced pick-up. devices individually adapted to pick up each of said signals with a time-displacement determined by the relative orientation 11f said devices with reference to the direction of each of said plurality of sources, a signal-indicating apparatus including means for scanning a. predetermined area in a field of parallel lines at a predetermined line-scanning frequency and for producing within said area an indication of any signal applied to said apparatus 'over a period of time considerably longer than the period of said signal, the position of said indication within said area being determined by the time of application'of said signal with reference to the scanning of said area, means for applying the signals picked up by said devices to said apparatus to cause said apparatus to produce a plurality of two-dimensional signal patterns in said field individually comprising parallel rows of signal indicia and individually representing the relative orientation of said devices with reference to the drection of. one of said plurality of sources, and means foradjusting the line-scanning frequency of said apparatus to cause said apparatus to produce a predetermined signal pattern comprising parallel' vertical rows of signal indicia representing the relative orientation of said devices with reference to the direction of said particular one of said plurality of sources.

19. A direction finder for determining the location of a source of radiated periodic signals comprising, a first plurality of pick-up devices, a

determined distance from said first-mentioned plurality,- the pick-up devices of each of said pluralities being spaced with respect to each other and being individually adapted to pick up said signals with a'time-displacement determined by the relative orientationof said devices with reference to the direction ofsaid source, signal-indicating apparatus including means for scanning a predetermined area and for producing within said area an indication of any signal applied to said apparatus over a period of time considerably longer than theperiod of said signal, the position of said indication within said area being determined by the time of application of said signal with reference to the scanning of said area, and

second plurality of pick -up devices spaced a premeans for applying the signals picked up by each of said pluralities of devices to said apparatus to cause said apparatus to produce a pair-,0! twodimensional signal patterns determined by the time-displacement of said applied signals and individually representing the relative orientation of the devices of each of said pluralities with reference to the direction of said source.

20. A direction finder for determining the location of a source of radiated periodic signals comprising, a first plurality of pick-up devices, a second plurality of pick-up devices spaced a predetermined distance from said first-mentioned plurality, the pick-up devices of each of said pluralities being spaced with respect to each other and being individually adapted to pick up said signals with a time-displacement determined by the relative orientation of said devices with reference to the direction of said source, signalindicating means comprising a pair of signalindicating apparatus each of which includes means for scanning a predetermined area and for producing within said area an indication of any signal applied to said apparatus over a period of time considerably longer than the period of said signal, the position of said indication within said area being determined by the time of application of said signal with reference to the scanning of said area, and means for respectively applying the signals picked up by each of sa d pluralities of devices to one of said apparatus to cause each apparatus to produce a two-dimensional signal pattern. determined by the time-displacement of said, applied signals and representing the relative orientation of the devices of one of said pluralities with reference to the direction of said source.

HAROLD M. LEWIS. 

